Did you used Dynamic websites before? you see its a good way for making fast admin areas for our websites?
Is it easy to customize? Is it easy for the end user to manipulate?
I am thinking to use it with a client and didn't use before, can you advice?
Yes I've used it.
Fundamentally if what you want to do is maintain tables as tables then its pretty much a yes across the board. Starting with a set of Linq classes (Linq to SQL or Linq to Entities) you get a mostly useable set of edit pages immediately.
You can then add custom field handling, pages, sort orders, most things you'd want.
Customisation is straightforward and can be developed over time - more importantly you change the database schema and keep your customisations intact.
Not perfect, but you get a huge amount of functionality for very little code.